In order to bond a conductive member such as metal and a nonconductive member such as wood by the adhesive, a technique for making the conductive member generate heat by an induction coil, i.e., a heating coil and for heating the adhesive is disclosed in Japanese Patent Laid-Open Publication No. 8-73818. Also, in order to bond the nonconductive members to each other, a technique for interposing between the nonconductive members a metal sheet to whose surfaces adhesive layers are applied and for heating the adhesive layers and bonding the nonconductive members by making the metal sheet generate heat by the induction coil is disclosed in Japanese Patent Laid-Open Publication Nos. 63-308080, 5-340058, and 6-100840.
In these techniques, when a high-frequency current is supplied to the induction coil, magnetic force lines of an alternating magnetic field generated by the induction coil penetrate the conductive member and the metal sheet and an electromotive force is created in the conductive member such as the metal sheet by the electromagnetic induction effect As a result, an induction current flows in the conductive member and the Joule's heat is generated and the heat is transmitted to the adhesive, so that the adhesive is heated. This electromagnetic induction heating device carries the high-frequency current in the induction coil to create an eddy current, whereby a particular portion can be quickly made to generate heat Therefore, by making the conductive members generate heat, interior materials and exterior materials of a building can be bonded to a building body in a short time. Simultaneously, the interior materials and exterior materials can be peeled off in a short time in remodeling the building, so that the peeled interior materials and exterior materials can be recycled.
When such an electromagnetic induction heating device is used, operation efficiency of assembling the interior materials can be improved in comparison with the cases of attaching the interior materials to a building frame by, for example, nails, screws, and rivets. More specifically, when the interior materials are to be assembled by nails or the like, heads of the nails protrude from surfaces of the interior materials, so that the heads have to be concealed by ornaments or the like and further noise is generated during construction. Meanwhile, when the solvent adhesive is used to bond the interior materials or the like to the building frame by the adhesive, the noise is not generated. However, it takes time to cure until the adhesive solidifies.
In contrast, when the electromagnetic induction heating device with the induction coil is made to heat and melt thermoplastic adhesive and then cool and solidify it, the adhesive can be not only heated and melted but also solidified in a short time, so that a time required for constructing the building can be largely shortened. As described above, it has been found out that an adhesive heating method for heating the adhesive interposed between the conductive member such as metal and the nonconductive member such as wood by the electromagnetic induction heating device and for bonding both members or, in order to bond the nonconductive members to each other, an adhesive heating method for interposing between the nonconductive members the metal sheet to whose surfaces the adhesive layers are applied, heating the adhesive, and boding both members can be applied for various uses, for example, the cases of assembling a large quantity of products such as automobiles and electronic devices and of bonding the sheet-like members to one another without being limited to the interior materials and exterior materials of the building. For example, regarding automobile parts or the like produced by combining resin members and metal members, a production time can be shortened and concurrently the used parts can be disassembled by melting the adhesive and be reused.
As a conventional electromagnetic induction heating device, a coil formed into a disk-like shape by spirally winding a coil material has been used. Generally, a little eddy current is generated in a portion of a conductor facing a center portion of such a spiral round coil and, consequently, the coil has the characteristic that heating temperature of the adhesive at a portion corresponding to the center portion becomes low. When two members are to be bonded by the adhesive, heating the metal sheet by using the conventional coil is limited to donut-shaped heating or heating dependent on a donut-shaped induced electromotive force and a shape of the metal sheet. Therefore, limit has been imposed on the heating of target regions of the metal sheets of various shapes. For example, in heating a rectangular tape, only both ends of a tape portion facing the coil center portion are heated, whereby an end-burnt phenomenon is caused and there is in a state of being not usable in practice. Countermeasures of the conventional techniques include a hole-strewed tape and a tape whose both ends are cut into wave-like shapes. However, these are insufficient as the burnt-end countermeasures, and involve risks of fire. For bonding of, for example, tiles that require wide-region bonding, there is no corresponding model among conventional devices, so that since these devices aim at only regions capable of being heated by the conventional coils, the heating of the center portion and corner portions becomes insufficient. In the bonding of tiles, the respective induction coils capable of corresponding to the heating of only edge portions and an entire surface are required.
Moreover, in order to melt the adhesive applied on the wide region in a short time, the large current has to flow in the induction coil. In the electromagnetic induction devices developed thus far, the current amount has been limited in terms of electrical power, heating efficiency is low, and control of the bonding region is limited. The present invention provides actually practical techniques which compensate for such problems of the conventional techniques.
Meanwhile, several techniques for utilizing iron cores in induction heating coils are known. Such an iron core depends on a kind and shape of a magnetic conductor, normal conductor, or the like used as unheated metal, so that the optimum polarity and shape of the core are specified with respect to heating conditions. In the conventional techniques, the core shape optimum to the heating conditions is not considered, and a U-shaped, E-shaped, or T-shaped core is uniformly used presently.
In the present invention, the magnetic poles and the shapes of a core portion can be changed under design in which a generation state of a magnetic flux loop relating to a magnetic flux emitting portion and a magnetic flux collecting portion of the core is considered with respect to the kind, shape, and position of unheated metal and to the heating conditions, whereby the above problems are solved. In terms of techniques, this is the same case as the case of changing of the position and polarity of the spiral coil. However, uniform heating of a large area, which cannot be performed by the conventional techniques, is prevented by such design that ends of the core are increased. Also, regarding control of the heating time, if the bonding portion is an ignitable member, over heating is extremely dangerous, so that detecting the heating temperature and controlling the supplied power are essential. The conventional techniques lack consideration for performing such strict heating control. The present invention provides specific techniques for solving the practical problems.